Cloud Watching Satellites Set for A.M. Launch

Oct 1, 2009

At 6 a.m. (EDT) on Friday, April 21, a Boeing Delta II Rocket will blast off from Vanderberg Air Force Base in Central California, carrying two satellites to add to the multitude already orbiting earth. The two new arrivals, CALIPSO and CloudSat, are a pair of Earth-observing satellites that are set to orbit earth once every 99 minutes on a mission to study clouds in the Earth's atmosphere. They will join what NASA calls the "A-Train," a constellation of five satellites (including CloudSat and CALIPSO) dedicated to studying planet's atmosphere. Already in orbit aboard the "A-Train:" the French satellite Parasol, measuring aerosols and clouds, is sandwiched between Aura and Aqua spacecraft which measures atmospheric chemistry, and water and energy cycles, respectively.

What's in a cloud?
Basically billions of visible liquid water droplets suspended in the atmosphere, clouds give us 2.5 percent of all fresh water on earth. But despite their ubiquity in daily life, scientists still have many unanswered questions about cloud formation, such as what is the exact mass of water and ice in clouds? Which clouds cause precipitation? How do clouds change with our climate? With the addition of CloudSat and CALIPSO, scientists hope to gather better data, augmenting their ability to analyze clouds and aerosols—small particles suspended in the atmosphere that act as the seeds for water droplets—and their effects on humans (from sunburn to the drive at five) and, similarly, our effect on clouds (pollution and climate change—the swim at five).

CloudSat
With a 94-gigahertz radar, the 8.3ft x 6.7ft x 7.5ft (with a 16.7ft wingspan) CloudSat sends radar pulses towards the Earth, measuring reflectivity and penetrability of clouds in the sky. These measurements can be used to calculate the altitude of clouds and the amount of water and ice in the clouds. CloudSat is powered by two solar array wings with a total solar array area of 64 sq. ft, producing 1,228 watts when closest to the sun (it averages 578 watts). The spacecraft has a 40 amp-hour battery backup for solar eclipses or load faults.

CALIPSO The CALIPSO spacecraft will gather data to allow scientists to make the first estimate atmospheric aerosol properties which modify clouds reflective properties as well as their life span) from direct measurement. CALIPSO uses three instruments: A light-detection and ranging instrument (LIDAR) provides high resolution vertical profiles of aerosols and clouds; An imaging infrared radiometer measures cirrus cloud particle size; And a wide-field camera takes pictures during daylight hours, capturing an visual meteorological image of scanned areas. This 1,294-lb., $298 million satellite will be collecting data on its primary mission for about 3-years, outlasting CloudSat by about a year, at cost of an additional $81 million.—Tyghe Trimble

Follow along with mission control here, and watch the launch live on NASA TV, available through most local cable service and on the internet at nasa.gov/ntv. Coverage begins at 4 a.m. EDT.

An exploded view of the Boeing Delta II set to launch from Vandenberg AFB tomorrow at 6 a.m. EDT.

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